Internally oxidized electrical contact



Unitedns a es a fl 'io .J L WRN LL -Q M EDE ECI A N T d ric R;- reb ll! a -ham; 6- sa e, ir fl t t burgh, Pa'.,. assignors :to... Gibso n Electric Company, i t-tte sorta Pa w e No Drawing. Application April 20, 1056 This i v i relates 0.. a. i ternal Oxidized trical contact generally most suitahlefor make and-break type-applications More. particular y,. it eon: eerns. an internally oxidized. silver-cadmium-zinc alloy which provides 5 advantages not, heretofore: attainable. Internal oxidation isna terrnavell known to th e fart, and, in this instance, refers;to.the selective oxidation of elements which alloy 'wi'th"'silver, f.which, oxidation penetrates progressively inwardly into the alloy at a rate de pending on temperature, time, oxy gen; oncentration and alloy composition. The oxygen is absorbed within the alloy and a uniform dispersiongof the oxide of the solute element is formed therein.

Electrical contacts". suitable. forrepetitive make-andbreak type applications must have, in addition to good conductivity, the" properties of 4 not welding or, sticking upon repeated opening and'elosing' of the circuit." Moreover, they must have a high resistance to wear and loss of material per operation must be low.

These results are not attainable with pure silver because of its softness, relatively low melting point and its tendency to weld or stick when interrupting overloads. To overcome this difliculty, many attempts have been made to .alloy silver with various other metals which are harder, stronger, and of higher melting point. It has also been proposed to mix other material with the silver by means of powder metallurgy techniques so that a mixture rather than an alloy is obtained. One material which has been added to silver contacts is cadmium oxide, which has been incorporated in the contact by powder metallurgy methods or by the internal oxidation of a silver-cadmium alloy. Such contacts, although they have been considered an advance over previous developments, are still found to be subject to the dangers of welding, sticking and excessive .arcing under more severe operating conditions.

The present invention overcomes these difiiculties by providing a contact in which the contacting surface comprises a mixture of silver, cadmium oxide and zinc oxide while the interior of the contact is a silver, cadmium, zinc alloy.

Accordingly, it is a primary ob ect of this lnvention to provide an internally oxidized electrical contact material which is particularly suitable for repetitive make-andbreak operations and which has outstanding qualities of wear resistance and resistance to sticking, fusing or weldmg.

This and other objects will become more apparent from the description which follows:

Essentially, this invention involves a novel electrical contact which is obtained through the internal oxidation of a silver-cadmium-zinc alloy. While it has been known to internally oxidize silver-cadmium alloys, it has been unexpectedly found that the three-component alloy provides results heretofore unattainable in silver-cadmium contacts.

Generally, the alloy composition will comprise by weight 80 to 95% silver, 5 to cadmium and an iemeq N .1 1.95s.

amount of zinc up to about of the cadmium, present. The alloy of this composition is then internally oxidized in air or anyother suitable oxidizing atmosphere at ele-- vated temperature, the time. and. temperature being'dependent on the desired depth of oxidationyas hereinafter setforth. p

Actually, the depth-of oxidation need only 'be superficial, i. e., of the order-of .001: inch up-to .005 inch,- when it is desirabIeto' maintain in the contact a greater proportion of -the' relatively strong unoxidized alloy, providefor 'more'economy in' the oxidation process; andat the same time dimin ishtheytendency of the-contact to weldorstick.

Although the zinc inthealloy does'not oxidize to zinc oxide as rapidly as the cadmium converts to cadmium oxide, it has beenfo'und that the addition of zinc: in our composition greatly improves the properties of the con operation to a minimum;

tact material whieh will a'll'owit to-open and close repeatedly on relatively-high currents without welding or' sticking; assist-in; quenching any arewhich-may exist'on opening the' circ ui t, and keeping the loss of material per The present material containing an internally oxidized silver-cadmium-zinc'alloy was compared with both internally oxidized silver-cadmium"materials 'and a pressed and" si'ntere'd silverr'cadmium' oxidecontact by identical tests carried'ou't in a 400 ampere, 7.5'volt, 3-poleD.-C. contactor. i 3 i The t able below shows the number of operationsobtained on eachof :these materials? Although the oxidized silvercadmiui n zinc alloy was wern,-it appeared that even at the end of the test runs there was some life left in these contacts. In the tests the load was shifted from pole to pole so that the contacts were subjected to electrical load only once for each three operations of the dev1ce.

The data above clearly indicate the superiority of the present contact in its ability to withstand repeated makeand-break duty. Thus, the contact of the present invention shows less tendency for sticking, welding or arcing and in general is more suitable for operations of this type.

The particular contact material used in the above tests contain 91 percent silver, 7 percent cadmium and 2 percent zinc prior to oxidation. After oxidation to a depth of .024.-025 inch, the internally oxidized portion would contain about percent silver, 7.5 percent cadmium oxide and 2.5 percent zinc oxide.

The contacts of the present invention may be produced in any suitable furnace supplied with an oxidizing atmosphere which may comprise either pure oxygen, air, or oxygen enriched air. The furnace temperature will generally be between 1400 F. and 1600 F. and the time of oxidation between one and sixty hours. Of course, the temperature-time relationship will vary depending upon the particular depth of oxidation desired.

For example, in one instance a temperature of 1600 F. for approximately one hour oxidized a contact of diameter and thick to a depth of .005. Other temperature-time data on the present internally oxidized contacts are as follows:

The internal oxidation may be superficial, as noted above, or complete. Ordinarily, however, it is preferred to limit the depth of oxidation to about .03- inch in order to minimize processing costs and retain a body of relatively strong unoxidized alloy in the contactstructure.

Although we have described a preferred embodiment of our invention, it will now be obvious that many modifications and variations may be made by those skilled in the art, and. we, therefore, prefer to be limited not by the description herein, but only by the appended claims.

We claim: 7

v 1. An electrical contact comprising an alloy of 85- 95% silver, 5l5% cadmium, and zinc present in an amount up to about 50% of the cadmium present, the contact surface thereof containing a mixture of precipitated cadmium oxide and zinc oxide.

2. An electrical contact comprising an alloy of 85-95% silver, 5l5% cadmium, and zinc present in an amount up to about 50% of the cadmium present, the contact surface thereof being superficially oxidized to contain a mixture of precipitated cadmium oxide and zinc oxide to a depth of about .005 inch.

3. An electrical contact suitable for repetitive makeand-break type applications consisting of an alloy of about 91% silver, 7% cadmium, and 2% zinc, in which the cadmium and zinc are internally oxidized to a depth of about .O24.025 inch.

4. The method of treating an electrical contact comprising an alloy of silver, cadmium, and zinc and containing 85 to 95% silver, 5 to 15% cadmium and zinc present in an amount up to about of the cadmium present to improve the 'wear and are resistance properties of the contact-making face of the contact, which comprises heating the contact in an oxidizing atmosphere at a'temperature of from 15.00" F. to 1800" F. for from one to sixty hours so as to oxidize the cadmium and zinc content of the alloy inwardly to a depth of up to about .030 inch.'.. J:

5. The method of treating an electrical contact comprising an alloy of silver, cadmium and zinc, and containing to silver, 5 to 15% cadmium, and zinc present in an amount up to about 50% of the cadmium present, which comprises heating the contact in an oxidizing atmosphere at elevated temperature so as to partially internally oxidize the'said contact; j

' 6. An electrical contact suitable for repetitive makeand-break type applications consisting essentially of {$5 to 95% silver, 5 to'15% cadmium, and zinc present in an amount up to about 50% of the cadmium present, the contacting face thereof being internally oxidized to a depth not exceeding .030 inch thereby forming within said oxidized portion, uniformly dispersed particles of cadmium and zinc oxide.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AN ELECTRICAL CONTACT COMPRISING AN ALLOY OF 8595% SILVER, 5-15% CADMIUM, AND ZINC PRESENT IN AN AMOUNT UP TO ABOUT 50% OF THE CADMIUM PRESENT, THE CONTACT SURFACE THEREOF CONTAINING A MIXTURE OF PRECIPITATED CADMIUM OXIDE AND ZINC OXIDE. 